As a water level measuring apparatus that measures the water level of a liquid stored in a liquid tank, there has been proposed a technique for indirectly measuring the water level based on a change in an interelectrode capacitance of a pair of electrodes arranged with a predetermined gap therebetween, as disclosed in Japanese Laid-open (Kokai) Patent Application Publication No. H11(1999)-311561 (Patent Document 1). Moreover, as a water level measuring apparatus that measures the water level by using another principle, there has been proposed a technique for directly measuring the water level based on a position of a float floating on a water surface, as disclosed in Japanese Laid-open (Kokai) Patent Application Publication No. 2006-170927 (Patent Document 2).